Application to Lead-Free Piezoelectric Ceramics
Next, this poling structure control technology was applied to lead-free piezoelectric ceramics. Generally, it is difficult to obtain lead-free piezoelectric ceramics that have a large piezoelectric constant, but it is also difficult to obtain lead-free piezoelectric ceramics that have superior resonance frequency temperature characteristics. Both cases require compositional phase boundaries, and this is because no other substances with compositional phase boundaries have been found besides lead-based piezoelectric ceramics.
We have conducted research and development on various types of lead-free piezoelectric ceramics, and we found that certain bismuth layer compound materials showed superior resonance frequency temperature characteristics irrespective of the compositional phase boundaries (see Table 1) .
The above-described poling structure design technology was applied to this material (SrBi2Nb22O9-based material) to achieve energy trapping and obtain practical resonance characteristics. The impedance resonance curve is shown in Fig. 5, and this shows desirable single-mode resonance characteristics.
Fig. 5 Impedance resonance characteristics of SrBi2Nb22O9-based lead-free piezoelectric ceramics
Table 1 Properties of various types of lead-free piezoelectric ceramics
|| (Li, Na) NbO3
|Bismuth Layer Structured
|| (Ba, Sr) 2NaNb5O15
|| (Bi, Na) TiO3
Conclusion: Future Materials Research and Development
The dispersion relationship that was presented in this paper was the relationship between the frequency and wave number, but if the frequency is generally taken as the amount corresponding to the energy, in terms of the solid-state physics theory, it can be considered to correspond to energy bands. We think that technology that achieves characteristics that were unobtainable before by controlling the structure in this way will take on growing importance in coming years.
We hope to utilize the recent innovations in nanotechnology for the microstructural design of substances and to control the energy bands to take on the challenge of creating new physical properties.
Original Paper: "Resonance characteristics derived by structural design of thermally stable piezoelectric ceramics," J. Ceram. So. Jpn. 118 pp.855-861, 2010